Contact less power supply systems include one which feeds electric power to “a plurality of working areas” from a primary-side induction line providing high frequency current. In the working areas, for example, a travel carriage is fed with electric power from the primary-side induction line though a pickup coil in a contactless manner.
In the system for feeding electric power to the “plurality of working areas,” it sometime becomes necessary, as at the time of maintenance of the working areas, to cut off the power supply for each working area. In such case, measures are taken by inserting a switching circuit in the primary-side induction line providing high frequency current, for each working area, and bypassing a within-working-area primary-side induction line led into the working area by means of the switching circuit when cutting off the power supply in the working area.
The switching circuit comprises a bypass circuit for bypassing the within-working-area primary-side induction line, and a switch adapted to switch to either the bypass circuit or the within-working-area primary-side induction line after the bypass circuit and the within-working-area primary-side induction line are simultaneously connected, whereby electric feeding to the other working areas being actuated is not cut off.
In the switching circuit, however, in order not to allow power to break down in the other working areas which are being actuated, it is necessary for the switch to ensure mechanical contact and contact duration in order for effecting simultaneous connection between the bypass circuit and the within-working-area primary-side induction line, and it is necessary, to this effect, to use a special and highly reliable switch. Further, if a power supply device is prepared for each of the working areas, such switching circuit can be dispensed with, but the cost becomes very high.
Further, when an lifting/lowering body, such as a crane, is fed with power from the primary-side induction line providing high frequency current, it is necessary that the primary-side induction line is capable of moving vertically in conformity with the lifting/lowering movement of the lifting/lowering body. To this end, the primary-side induction line is allowed to slack so as to be movable vertically in conformity with the lifting/lowering movement of the lifting/lowering body.
However, when the crane or other lifting/lowering body is fed with power from the primary-side induction line providing high frequency current, a wire breakage tends to occur in the primary-side induction line as the line repeats lifting/lowering movement with the lifting/lowering body. Thus, in order to avoid power breakdown occurring in all power supply lines due to such wire breakage, frequent maintenance is necessary.